With the increased application of lithium ion secondary batteries in automobiles and hybrid automobiles, a higher energy density is required.
In general, each of a positive electrode and a negative electrode of a nonaqueous electrolyte battery is obtained by coating a slurry containing an active material on a metal foil of aluminum or copper. In order to make the energy density higher, it is necessary to make the metal foil thinner, and to make the electrodes smaller and lighter. However, when the metal foil is made thinner, there is a problem that the mechanical strength of the electrode tends to be deteriorated to result in fracture. In particular, an electrode located on the outermost layer that is a collector tab fixing part in an electrode group is likely to be affected by stress more than other portions, resulting in fractures, which deteriorates a battery capacity, and an increase in the internal resistance.